Beam forming apparatus



Filed March 25, 1963 BEAM FORMING APPARATUS 7 Sheets-Sheet 1 ALLA/v 0, A e VA/VT/NE INVENTOR.

Dec. 21, 1965 A. D. LE VANTINE 3,225,188

BEAM FORMING APPARATUS Filed March 25, 1963 7 Sheets-Sheet 2 70 A j B /76 F ygi y 62 r r; I o F2 84 78 RELATWE INTEN5\TY lOO ALLA /v 0. L e (/A/VT/NE INVENTOR.

I A77'ORNE Y Dec. 21, 1965 A. D. LE VANTINE BEAM FORMING APPARATUS 7 Sheets-Sheet 5 Filed March 25, 1963 ALLA/v D. ZQI/ANT/NE INVENTOR Dec. 21, 19.65 A. D. LE VANTINE 3,225,138

BEAM FORMING APPARATUS Filed March 25, 1963 I 7 Sheets-Sheet 4.

us 10/a/ ALLA/v .0. LeVAA/T/NE INVENTOR.

A WORN/5y Dec. 21, 1965 Filed March 25. 1965 A. D. LE VANTINE BEAM FORMING APPARATUS 7 Sheets-Sheet 6 ALLAN 0. L e l/ANT/NE INVENTOR.

A 77'ORNEY Dec. 21, 1965 A. D. LE VANTINE 3,225,188

BEAM FORMING APPARATUS Filed March 25, 1963 7 Sheets-Sheet 7 SCAVENG\NG R\NG RAY?) F RO M CON\CAL R\N6 INVENTOR.

lf/ 2w 5% A FOR/WE) o Q ALLAN .0. Lel/ANT/NE United States Patent 3,225,188 HEAM FORMING APPARATUS Allan D. Le Vantine, Tarznna, Calif., assignor, by mesne assignments, to TRW Inc., a corporation of Ohio Filed Mar. 25, 1963, Ser. No. 267,702 6 Claims. (Cl. 24041.l)

My.invcntion relates to light beam forming systems and apparatus, and more particularly to high intensity light beam forming apparatus for providing radiation which approximately corresponds to that .of the sun. More specifically, the present invention, in one of its aspects, relates to improvements in apparatus of the general class described in my copcnding patent application, Serial No. 216,677, filed August 13, 1962, and entitled Radiation Beam Forming Apparatus. For a variety of applications it is desirable to provide a beam of radiation in which all of the rays are substantially parallel. That objective is not particularly formidable in the ordinary case; however, it becomes difficult to achieve when high efficiency is desired and when uniform field illumination over an area exceeding a few square feet is required.

While it should be understood that apparatus in accordance with the present invention is not limited to any specific industry or field of application, it may be most conveniently and understandably described by reference to one particular embodiment which is particularly useful for laboratory testing and evaluation of the thermal characteristics of spacecraft in a simulated space thermal environment, The sun impresses approximately 1400 watts of radiant power on each square meter of the surface of the earth facing the sun. To duplicate that radiant energy on'a 10 ft. diameter area in the laboratory, for example, would require over 10,000 watts of light power. Because of the inherent low efiiciency of practically all devices for converting electrical energy to light, the production of such magnitudes of light power having spectral distributions comparable to sunlight and. a reasonably similar collimation characteristic usually requires to 50 times the input electrical power. To additionally assure that the beam intensity is the same over the entire cross-sectional area requires substantial improvement over the prior art of which I am aware.

The above mentioned copending application describes one apparatus which develops a beam of light having generally thedesired intensity and collimation characteristics. Briefly, that application teaches a system which includes an improved carbon arc lamp generally similar to the type used in moving picture projectors and an improved high efficicny optical arrangement for collecting and collimaling a large portion of the radiant energy produced by the-electric are. While that apparatus is satisfactory and has been used with considerable success, it is somewhat limilcd in performance by the fact that the light collecting reflector assembly is located behind the carbon are so that the output light beam is required to pass through and around the electric arc and the associated mechanical apparatus, resulting in blockage of light, so that the systems efiiciency is less than ideal. A substantial improvement in efliciency can be achieved by systems which avoid the foregoing difficulty.

Accordingly, it is a primary object of the present invention to provide ahigh intensity beam forming apparatus having improved beam collimation and relatively high cfficiency light collection capabilities.

It is another object of my invention to provide improved apparatus which produces a beam of radiation having collimation characteristics approximately like that of the suns rays and producing substantially uniform light intensity at all elemental portions of a predetermined illuminated area.

It is a further object of my invention to provide an apparatus which produces substantially uniform light intensityover an area of several square feet, a spectral energy distribution approximating that of sunlight, and a degree of ray collimation which is sufficiently like that of sunlight to avoid large discrepancies in the thermal effect of the rays on objects irradiated thereby.

lt is a different object of my invention to provide means for generating a beam of solarlike radiation which may be used in simulating the thermal environment encountered by an object located outside the earths atmosphere.

It is one general object of my invention to provide an economical apparatus of improved efficiency for developing a high intensity beam of light energy in which the intensity is substantially equal at all elemental portions of a plane normal to the longitudinal axis of the light beam.

It is another general object of my invention to provide improved apparatus for simulating high altitude and outer space thermal conditions. i

In accordance with a preferred system utilizing the concepts of my invention, an apparatus for simulating high altitude environmental conditions includes a large cylindrical vacuum chamber adapted to receive an object such as a space vehicle or satellite which is to be subjected to emperical analysis of its thermal characteristics. Associated with the vacuum chamber is radiation beam forming arrangement for applying to the test object a beam of radiation similar to sunlight. Preferably the beam forming apparatus is located externally of the vacuum chamber and transmits a beam of light through a window member in one wall of the chamber for irradiation of the test object by way of a reflector contained within the chamber. In a preferred form, the light source comprises a carbon are lamp and a light collecting arrangement positioned adjacent to the are for elhcicntly directing a major portion of the are light along the light path to the test object. In order to achieve optimum uniformity of the light intensity across the area to be illuminated, the light collecting structure preferably comprises a plurality of concentrically arranged reflective surfaces of dillcrcnt mean diameters. The different reflective surfaces preferably are spaced different distances from the carbon are along the axis of the light beam in a manner such that the radial distances from the carbon arc to corrcspomhng portions of the different reflective surfaces are substantially equal. More specifically, in accordance with one embodiment of my invention wherein the carbon arc has a more or less cardioid shaped polar intensity pattern. the different reflective surfaces are positioned so that corresponding portions are at approximately equal but slightly different distances from the light source, with the departure from distal equality being in a direction to cause the corresponding portions to lie along a curve of constant light intensity. The apparatus of my present invention differs from that of my aforementioned copending application in various respects. One such distinction is that the light collecting reflective and refractive structure is positioned in and around the light beam path on the same side of the light source as that from which the beam path extends. With this improved arrangement of the light collecting structure, no portion of the reflcctivcly collected light beam is required to pass through and around the region of the arc and associated structures. Accordingly, absorption by these elements is avoided anduniformity of the light beam intensity is optimized.

In accordance with another aspect of the present invention, the light beam, after entry into the vacuum chamber, is projected to one or more collimating reflective surfaces which preferably are off-axis parabolic sections supported on the interior wall of the vacuum chamher. The reflective surfaces are constructed to have a. sufliciently low thermal cntittance to make the thermal radiation from their surface substantially negligible compared to that from other portions of the walls of the vacuunf chamber. The use of such collimating off-axis parabolic reflecting surfaces is particularly advantageous in that it prevents infrared radiation emitted by the test object from being reflec ed back to the test object. That is. in order to simulate space conditions, with reasonable accuracy it is necessary that the simulation facility be arranged so that the object being tested cannot see itself in any surface which would rellcct visible light or infrared radiation. A warm object in outer space emits thermal radiation and reflects visible light into infinite regions of deep space and thereby disposes of large quantities of energy. To duplicate that condition it is practically essential that a test object in a simulation chamber be permitted to see only a cryogenic surface which has radiation absorption characteristics approximating deep space.

These and other objects of this invention will be ap parent from the following description taken with theac companying drawing, throughout which like reference characters indicate like parts, which drawing forms a part of this application and in which:

FIG. I is a plan view, partially cut away, of a space environment simulation vacuum chamber in accordance with my invention for receiving an object to be cnviron- .mentally tested;

FIG. 2 is an elevational view of the apparatus of FIG. 1;

FIG. 3 is a sectional view taken along the lines 33 of FIG. I and showing the interior structure of one end of the chamber;

FIG. 4 is a diagrammatic illustration of a conventional arc lamp light collecting structure whiclris useful in ex plaining the limitations of such structures and the advantages of the present invention;

FIG. 5 is a diagrammatic illustration of the light collect- I ing arrangement of the present invention;

FIG. 6 is an end view of the multisurface light collecting structure of my invention. taken from a position looking along the central axis of FIG. 5;

FIG. 7 is a side view partly in section of the structure illustrated in FIG. 6;

FIG. 8 is a perspective view of the apparatus illustrated in FIGS. 6 and 7;

FIGS. 90 and 9b are side views of one of the reflector elements of the multi-surface light collecting structure shown in FIGS. 6, 7 and 8;

FIGS. Illa and 1011 are side views of a different one of the reflector elements of the multi-surfacc structure shown in FIGS. 6, 7 and 8;

FIG. II is a diagrammatic illustration of the optical system of the apparatus shown in FIGS. 1, 2 and 3 and including diagrammatically the multi-surfacc reflective structure illustrated in FIGS. 6, 7 and 8;

FIG. 12 is a front view, partially broken away. of the graduated screen ftltcr shown diagrammatically in FIG. ll;

FIG. 13 is an enlarged end view of a beam intensity conlit 4 trol means which forms a part of one embodiment of the system illustrated in FIGS. I and 2;

FIG. 14 is a side view of the apparatus shown in FIG. 13;

FIG. 15 is a diagrammatic illustration similar to FIG. ll of another embodiment in accordance with my invention.

In apparatus for simulating the thermal effects of solar radiation it is necessary to illuminate a substantial portion of the interior of a vacuum chamber with light having a spectral distribution generally similar to that of the sun within the wavelength range from 0.2 to 3.6 microns. Preferably, the light beam should have substantially uniform intensity at every elemental portion of the target area. The apparatus of my invention provides excellent spectral distribution, uniform field intensity, and a higher efficiency than any existing comparable apparatus of which I am aware. In order to duplicate the thermal effects of the sun in a laboratory vacuum chamber of limited space, critical attention must be given to the problems of collimating the rays of light and achieving uniformity of light intensity across a plane normal to the light beam direction. The most practical means for converting larger quantities of electric power to light energy with a spectral distribution reasonably comparable to sunlight is a carbon arc lamp of the general type commonly utilized in moving picture projectors. For example, a 13.6 mm. D.C. carbon arc lamp using carbon electrodes to which appropriate salts have been added, and operating at approximately volts and 160 amperes, will produce light energy across the wavelength range from 0.2 micron to 3.6 microns with the energy distribution being a close approximation to the energy distribution of solar radiation before attenuation by the earths atmosphere. The efficiency of a carbon are using 13.6 mm. diameter carbon electrodes is about 34%. The radiation is emitted in a polar distribution which may be roughly represented by a cardioid of revolution wherein a radius vector denotes the light intensity. Specifically, if the intensity at the direction of maximum light intensity is considered as being the radiation intensity at the periphery of a solid angle of 70 is about 40 to 50%. To achieve reasonable over-all elficiency of the system it is most desirable that the light collecting arrangement be adapted to gather and utilize substantially all of the light energy within that solid angle.

GENERAL DESCRIPTION An improved system embodying light sources having the foregoing characteristics and an improved beam forming arrangement for directing light energy to a test object in a vacuum chamber is illustrated in FIGS. I and 2. The apparatus comprises an elongated cylindrical tank 20 having a hinged end bell 22 to provide access to the chamber interior in which a test object 24 such as an aerospace vehicle may be positioned for evaluation of its thermal charaeterist's The test object 2-l is normally positioned near one end of the chamber 20 and is preferably surrounded by a liquid nitrogen cooled liner which includes sections 26, 2S and 30. Such cryogenic liner structures are well known in the art and, accordingly, are not described in further detail except to emphasize that they provide a heat sink for absorbing substantially all infrared and visible light emanating from the test object. At one end 32 of the chamber there is located a collimator assembly comprising a plurality of oil-axis parabolic reflector members 34, 36, 38 and 40 which are oriented at different angles relative to the longitudinal axis of the vacuum chamber. Specifically, the dilfcrcnt reflectors 34, 36 and 38 and 40 are positioned to individually receive light from different ones of a plurality of beam forming lamps 42, 44, 46 and 48. The optical axis of the lamp 42, for example, is oriented so that a light beam projected therefrom and impinging on the reflective surface 34 is redirected by that surface in a direction substantially parallel to the longitudinal axis of the vacuum chamber.

i of the vacuum chamber.

The off-axis parabolic reflectors 34, 36, 38 and 40 are preferablyfront surface coated with aluminum (by a vacuum deposition technique) to provide the reflective surface with a very low infrared cmittance characteristic so that the offaxis parabolic surfaces may be maintained at a relatively high temperature as compared to the cryogenic temperature of the surrounding liner members 26, 28 and 30. Even though the parabolic reflecting sur faces are relatively quite warm during'operation, the thermal radiation emitted by these surfaces is negligible compared to the infrared radiation impinging on the target object from other portions of the chamber. These reflective surfaces 34, 36 and 33 preferably operate at approximately the temperature of the outer wall of the chamber so that diflicnlties with thermal distortion of the mirror surface are avoided and so that there is a reduced tendency for vapor and other foreign substances to condense on the parabolic mirror surface. As stated heretofore, it is desired that the test object shall see a deep space environment in all directions 50 that the heat sink surrounding the object 24 will have substantially the same heat sink characteristics as deep space. Use of the off-axis parabolic reflective surfaces 34, 36 and 3S achieves that result byproviding an arrangement whereby a beam of light energy may be introduced into the chamber and directed to the test object 24 while, at the same time, thermal radiation emanating from the test object will not return to the test object but will be reflected from the parabolic reflective surfaces to various portions of the cryogenic inner liner 26 and 28 of the chamber; that is. the geometry is such that any ray originating from the test object will reflect from one of the surfaces 34, 36, 38 or 49 and will be absorbed by the cryogenic wall so that the energy is not returned to the test object. The parabolic collimator surfaces 34, 36, etc. preferably are maintained at an absolute temperature of about 300 Kelvin and have a surface cmittance factor of 0.04. In one particular caseit has been determined that the thermal radiation errors due to the use of liquid nitrogen cooled chamber liners 26 and 23 to simulate the heat sink of space are negligible for practical purposes. For a test object temperature of 300 Kelvin (80 F.), the error, as compared to absolute space, is about 0.5% for the liquid nitrogen cooled liner members 26 and 2S and is about 0.8% for the parabolic reflectors 34, etc. object temperature of 245 iclvin (-20 E), the error is maximum of about 3%. At a test object temperature of about 200 Kelvin, the thermal departure from outer space conditions is somewhat less than 7%.

The operating temperature of the parabolic collimators 34, 36, etc. is maintained within satisfactory non-distorting limits by providing a high cmittance coating on the rear surface of each of the collimators 34, 36, 38 and 49 (FIG. 3) and on the structural support members 50 and 52 by means of which the collimators are affixed to the outer end wall 32 of the chamber. A flat black epoxy paint having an cmittance of about 0.92 in the infrared wavelength range has been used successfully for coating the rear surfaces of the collimators 34, 36, 38 and 40. The temperature of the collimators will rise about 30 to 40 degrees l. above the chamber wall when the apparatus is operating with a high intensity light beam falling on the collimators. With the bcamstrom the lamps 42. 4% turned off, the temperature of the collimators drops only about 3 F. below the temperature of the outer wall 33 'l his relatively small variation in the operat ng temperature of the parabolic collimators 3-1, 3(. 3S and 40 is small enough so that temperature distortion of the parabolic surfaces doesnot create a problem. Additionally, operation of the parabolic collimators at a temperature considerably higher than the surrounding chamber walls prevents condensation of vapors on the reflective surface.

As stated heretofore, each one of the parabolic collimators 34, 36, etc, receives an input light beam from With a test a separate lamp assembly. The solar radiation simulation facility may utilize, depending on size and light intensity requirements, any selccted number of similar lamp units 42, 44, etc. and individually cooperative parabolic collimators 3 35, etc. The exemplary apparatus of FIGS. 1 and 2 has four such lamp units 42, 44, 46 and 48 with two lamp units located on each side, one above the other. Each lamp unit directs a slightly divergent light beam toward the vacuum chamber along a central axis 54 which intercepts the chamber wall at an angle of about The light beam is transmitted through the chamber wall by a projection lens 56 which provides a vacuum tight light transmissive entrance port in the chamber wall. The entrance port lens 56 is supported on an angularly disposed portion of the tank wall and is secured thereto by means of a vacuum tight sealing arrangement which preferably includes a conventional O-ring. One such arrangement is illustrated and fully described in my above-mentioned copending application. Accordingly, the same is not described in detail herein. The light beam which is projected into the vacuum chamber through the entrance port lens 56 and along the central axis 54 is provided by the externally located lamp unit 44 which is described in detail in the following.

THE BEAM FORMING LAMP UNIT Each lamp unit 42, 44. etc. comprises a housing 53 which encloses a carbon are light source and an improved arrangement for collecting the light and projecting the same along the optical axis 54 toward the parabolic collimator 36. Generally, the lamp housing and the mechanisms for continuously feeding the carbon electrodes are similar to various moving picture projection lamps which are well known in the art and commercially available.

For example, one such projection lamp is manufactured and sold by the Strong Electric Corporation, 87 City Park Avenue, Toledo, Ohio, as their model number U-l'l l. Accordingly, the structural arrangement and operation parameters of the electric arc mechanism are not described in detail. The lamp assembly of the present invention differs from conventional moving picture projection units in two significant respects. Firstly, I prefer to orient the negative carbon and its support and feed mechanism substantially at right angles to the axis of the positive carbon so that the negative carbon and its associated fccd mechanism do not block the path of light rays from thcclcctric arc to the light collecting structure. Secondly, in conventional moving picture projection units, light from the arc is normally collected by a reflector on the opposite side of the are from the positive carbon and is reflected therefrom along a light path which extends from the positive carbon end of the lamp unit. In contrast, in accordance with my invention, the light rays are not reflected back through the are but rather are collected by a reflective and refractive light collecting structure referred to hereinafter as the tansflector and projected outwardly from the end of the lamp unit which is on the opposite side of the are from the positive carbon. This feature has the very important advantage that partial blockage of the collected light by the structures in the vicinity of the are is complct-cly obviated in that the collected light beam does not have to traverse the region of the arc. This feature of my present invention will be better appreciated by first briefly considering the magnitude of the problems encountered in solar simulation apparatu and the limitations of the arc lamp arrangements which have been used hcrctofore.

As noted heretofore. a practical solar simulator demands on the order of 10,000 watts of radiant power to cover a 10 ft. diameter test area. Even if all the light emanating from an arc lamp were utilizable, the total input electrical power would have to be something in excess of 30 kw. In actual practice, the best parabolic or elliptical reflectors which have been used heretofore in conjunction with are lamps are capable of collecting light from a solid angle of only about The result is that a Sllbtlflfllltll portion of the light emanating from the electric arc is wasted. and hence, the over-all efliciency of such prior art beam forming lamps is extremely low.

Production of tens of thousands of watts of light power with such low-efficiency apparatus becomes prohibitively expensive in terms of power supply apparatus, to say nothing of the problem of dissipating the excessive heat energy developed by the low cfliciency apparatus. In contrast, a system in accordance with my invention can irradiate an extended area with intensities up to about 275 watts per square foot with 10% of the input electrical power being delivered to the test area as radiation having a spectral distribution substantially corresponding to that of sunlight. This 10% over-all efficiency is several times lcttcr than the efliciency of arrangement proposed heretofore which usually employ transmissive optical systems and which do not utilize the multisurface reflective light collecting structure as described hereinafter.

Moreover, conventional elliptical or parabolic light collecting reflectors which have been used in motion picture projection lamps do not readily provide uniform. light intensities over an extended area and, consequently, are not satisfactory for use in solar system apparatus. 'To illustrate this limitation of prior art arrangements there is shown diametrically in FIG. 4 a conventional elliptical reflector positioned behind the are crater 72 for collecting the light which emanates from the crater 72 and for directing the same generally along a central axis 74.

As shown in FIG. 4, the diameter 5 of the light source or are crater 72 is indicated by the numeral 76. Light emanating from the are crater 72 and reflected from an incremental portion 78 on the surface of a reflector 70 has a dispersion pattern as indicated by the central ray 80 and the limiting rays 82 and 84. The area 6 over which that light is dispersed at the second focal plane 86 depends, of course, on the diameter 6 of the light source. In addition, from FIG. 4a it will be appreciated that the diameter of image 6 at the second focal plane 86 is dircctly proportional to the distance from the particular reflective point 73 to the second focal plane 86 and is inversely proportional to the distance from the source 72 to the particular reflective point 78. In a conventional system, as illustrated in FIG. 4a, utilizing a conventional elliptical reflector 79 and a light source 72 of finite diameter. rays reflected from a point near the center of the elliptical reflector 70 will be dispersed over a larger area at the sccond'focal plane 86 because of the fact that the radial distance r from the source 72 to the reflector 70 is smaller for points near the center of the reflector. That is, since 6 is inversely proportional to the radial distance r the image size produced at the second focal plane by rays reflected from points further from the center of the elliptical reflector 70 will be smaller than those reflected from nearer the center of reflector 70. This means that in an apparatus using a conventional elliptical reflector, a distinct image of a finite source, 5 of reasonable size, cannot be formed. And even if 6 were a spherically radiating source of Lambert characteristics the image uniformity would not be conserved at the second focal plane. F tltltl). The relative intensity varies substantially as shown by the curve 83 in FIG. 4b. 'l'hat result is to be avoided in solar simulation apparatus since a primary object of such apparatus is to provide uniform light intensity across the area illuminated.

In accordance with my invention, as illustrated diagrammatically in FIG. 5, the light collecting structure 9t comprises a series of concentric rings 91, 92. 93, etc., having polished specular inner surfaces. Ideally, the rings 9!, 92, 93, etc. should individually be segments or sections of different ellipsoids of a family of ellipsoids which all have foci at F and F In actual practice the rings may be terroidal sections (i.e., segments of a body of rotation of circular cross section whose circular axis does not coincide with the axis of rotation) approximating the ideally more exact ellipsoidal surfaces. 50 long as the axial width .3,- of each ring 9l99 is relatively very small compared to its mean diameter, very little deterioration results from the use of the more readily manufacturable torroidal section rings. In accordance with one embodiment of my invention, the light collecting structure 90 overcomes the above stated limitation of conventional arc lamp reflectors by having the rings 9199 arranged so that they are all substantially equidistant radially from the light source 72. This important feature of my apparatus causes each ring 9L5? to receive light of substantially the same intensity from the source 72 so that the different rings ).l99 all illuminate the second focal plane 100 with light of equal intensity to thereby provide a uniform field of illumination at the second focal plane. Specifically, the rings 91-99 are positioned concentrically about the central axis 102 and with the planes of their means diameter circles being normal to the axis 102-, the ring 9*) which has the smallest transaxial diameter is positioned a maximum distance along the axis ['32 from the source 72. The next larger diameter reflective ring )3 is positioned a lesser axial distance from the source 72 such that the mean radial distance r is equal to the mean radial distance r from a corresponding portion of the first reflective ring 99. The successively larger reflective rings 97, 96, 95, etc. are positioned at successively lesser distances along the axis 102 from the source 72 so that mean radial distance of each ring from the source is substantially equal to the mean radial distance 1' By this arrangement, rays reccted from the mean diameter points of the different reflective. surfaces are caused to form an image of substantially the same diameter at the second focal plane In accordance with the equation by holding the radial distance from the source 72 to each one of the reflective surfaces equal, the different images 5 at the second focal plane 1th) are held substantially the same so long as I: is long compared to 1' If, in a particular apparatus r is not very large relative to r then the image size can be maintained approximately constant by holding the ratio r zr constant for all of the ring elements. At the second focal plane 190, all rays from the rings 9l-99 converge to form a least connnon circle. The field intensity across this least common circle from a source 5 of uniform intensity is substantially uniform. In accordance with one embodiment of my invention. the smallest reflective ring 99 has a diameter of about 6% inches. positive projection lens 164 for collecting the light rays within a three inch radius circle surrounding the central axis 102- and retracting tho e rays sufhcicntly to direct them to the second focal plane lift). preferably constructed to have focal points at F and 1 so that it serves in conjunction with the rings 91-9) to provide collection of all the light rays emanating from the source 73 through a solid angle of about and projecting all those rays to provide a beam of uniform intensity at the second focal plane tilt). Use of the lens 164 for collection of the li -ht rays in the central region is desirable in that it can be made more cflicient than a plurality of small diameter reflecting rings having finite thicknesses in the transaxial direction. A preferred material having a high transmissivity in the wavelength range of interest which may be used for the lens 164 is a fused quartz sold by General Electric Company and designated as their type No. 105.

While my invention has been described in the foregoing with rcfcrcncc to one specific form. it will be appreciated that the concepts are not limited to that particular apparatus. For example in a further embodi- Inside that ring there is provided a i The lens l'lld is ment of my invention the light collecting structure 90 is constructed and arranged so r varies from ring to ring in a manner such that the light intensity impinging on a selected elemental portion is substantially equal to the intensity at a corresponding portion of any other ring. In other words, the relative physical position of the rings are such that they lie along a curve of constant intensity. This embodiment is particularly advantageous for those applications where it is desired to provide a field of uniform flux emanating from the light collecting structure 90.

The multisurface light collecting structure 9t} which has just been described with reference to the diagrammatic illustration in FIG. 5 is shown in further structural dctail in FIGS. 6, 7, 8, 9 and l0. This structure 99 is light transmissive in the sense that the collected light which is reflected by the ring 91. for example. passes through the aperture between the rings 9t and 92. Similarly, the light collected and reflected by ring fil passes through the interstitial space between the rings 933?. Thus the transmissive multisurface reflective light collecting assembly may be appropriately and conveniently referred to as a transtlcctor for collecting light from a large solid angle and directing the same in a beam of uniform cross-sectional intensity to an approximate focus at the second focal plane 1%. While the trans fle'ctor 90 has been heretofore described as comprising nine concentric rings, in actual practice I have found it desirable to use as many as 32 concentrically arrayed rings as shown in FIGS. 6 and 7. The transt'lector 90. including the concentrically spaced-apart rings 93, 94. etc.,.is structurally integrated by a plurality f radially extending support brackets 106 angularly spaced around the assembly and supported at their outer ends by attachment to a heavy support ring Hi8 which may be secured to the lamp housing in a manner to support the transtlector 90 concentrically about the optical axis ltl'd. The radially extending support brackets It'll; are slotted on their inside edge or left hand edge as seen in FIG. 7 so that a separate shoulder lit) is provided for receiving each one of the reflective rings 92. 93, 94, etc. The innermost ends 112 of the brackets 106 engage and support quartz lens 104 so that it is concentrically positioned relative to the optical axis 102. Details of the reflective rings 92, 93. 94. etc. are shown in FlGURl-TS 9a and 9b and FIGURES 10a and 101'; wherein FlG- URES 9a and 917 represents one of the larger diameter rings which preferably is machined from aluminum alloy plate. As indicated by the character R in FIGURES 9a and 9b, the reflective inner surface of the larger rings 92, 93, 94. etc., is machined to have a radius of curvature which substantially exceeds the minimum diameter of the ring 92. The distance of the center of curvature from the leading edge 116 is designated by the character A, and the maximum diameter of the rcfiective inner surface is designated by the character B,

while the character C designates the Width of the insurface diameter of 17.02 inches whi e the twentieth ring from the outside of the transilector assembly has a reflective surface diameter of approximately 8.2 1 inches with the IS rings which intervene between those two have successively smaller diameters from U14 inches to 8.44 inches. The dimensions specified by the following Table I are given by way of example on y as illustrative of one of several apparatuses which 1 have constructed and utilized in accordance with the concepts of my invention. It will, of course, be understood that the present invention is not to be construed as being limited to the specific dimensions specified or to any one of them.

ill

10 Table I Ring NO.

As shown in FIGS. ltla and ltlh, the twelve innermost of the transllector assembly have surface diameters designated by the letter K and have the reflective su face anguiated relative to the central optical axis as indicated by the character H. These smaller diameter rings pre rably are formed by cutting one-quarter inch v. to curvilinear strips from sainlcss steel sheet material of, about .020 inch thickness and then forming the curvilinear strips into circles and welding the ends together. The res-p live rings are required to have a slightly larger inner diameter K at the right hand side as compared to the diameter at the left band edge. To achieve that result it is neces-ar to use strips which are cut along dif rent radii, as indicated by the character L in Table Thus the fol owing Table II specifics by the char- Table II fling No.

As shown diagrammatically in FIG. 11, the transl'ieetor 90, including the lens 184, is positioned concentrically and symmetrically about the centralaxis of the light leam path and is spaced from the center of the carbon are plasma light source 266 a distance such that it subtends a solid angle of about 140 degrees with respect to the light source. As stated heretof0re,'the negative carbon 204 is oriented vertically or substantially at right angles to the optical axis .293. The positive carbon 202 is aligned with the optical axis 203 and on the opposite side of the light source 206 from the translleclor 90. Since the plasma light source 206 is relatively close to the translleclor 9t, it must be considered as a light source of finite diameter. ljzlit emanating from the sourccltlfa and falling on a particular elemental portion of the inner surface of a ring 91 is indicated by the limiting rays 20S and 210. These limiting rays are reilccted front the ring 91 to provide at the second focal plane F a dispersion pattern which depends on the nor 7 diameter of the light source, the distance of the ring H from the source, and the distance from the ring Fl to the second focal plane F As stated hcrtoforc, the sire of the image provided by each ring is maintained approximately the same by the structural arrangement of the transtlcctor in which corresponding portions of the different rings 92', 93, 94, etc., are approximately cq'. idistant from the light source. Additionally, the distal equality of the different reflective rings assures that the light intensity falling on corresponding portions of the different rings is substantially equal so that the transflector provides a beam at a first focal plane 211 in which all elemental portions of a cross section of the beam are of substantially equal intensity. That is, the transtlector 90 will provide a uniformly lighted surface at the plane 211.

There are practical limitations relating to the oricntation of the transflector )9 with respect to the light source 206. If the angle of coverage of the source is repr sented by 17 there is some minimum value and some ma iimum value for p outside of which the transllcctor conc"pt would not be useful. The maximum ur cful value of is the angle where the intersection of the limiting my 208 and the limiting my 213 form a 90 degree angle. The minimum value for 1/) is the angle at which the smaller diameter rings of the transttcctor become so closely spaced together that the physical thickness of the rings blocks a substantial quantity of the impinging radiation and thereby causes the individual ring to be less efiicient than a corresponding annular segment of a refractive element such as the lens 104. Thus, provision of the lens 104 in the central region of the transtieetor assembly 90 results in a eombinationwhich is considerably more efficient than would be a further inward extension of the concentric ring arrangement.

If desired, a system in accordance with the present invention may be provided with a variable diameter iris 216 positioned at the second focal plane. Because of the dispersion technique which is utilized in apparatus in accordance with my invention, the variable diameter iris 216 will not reduce the diameter of the beam at the target object 222 but rather the iris 216 operates to continuously vary the uniform radiation intensity from a maximum corresponding to the maximum energy output of the sys tem to zero intensity when the iris 216 is fully closed. In some systems using the concepts of the present invention it is inconvenient for practical reasons to provide a variable iris such as the element 21:? of FIG. ll. ln arrangements where such an iris cannot be used or cannot conveniently be positioned at the second focal plane F a substantially different beam intensity control arrangement, which will be described in further detail hereinafter with reference to FIGS. 13 and 14, has been used with considerable success. v

As shown in FIG. It, the optical system further includes a projection lens 213 which may be formed of material similar to that mentioned above for the first projection lens 184-. The second projection lens 213 is supported in an aperture in the wall 219 of the vacuum chamber and thus serves not only as a lens for improving the collimation of the light beam but also as a transmissive entrance port in the vacuum chamber. partially collimatcd light beam as projected along the optical axis 203 to the right of the entrance port lcns 21S impinges on a parabolic mirror or rct'lccting surfacc 27.0 which corresponds to one of the parabolic collimators 34, 36 and 38 of the apparatus of FIG. 1. The parabolic reflecting surface or collimator 22f) serves to further collimatc the beam so that the beam between the collimator 220 and the target object 222 consists of substantially parallel rays. ln a preferred embodiment of the invention. the collimation of the light beam as it impinges on the target object is within 1 degrees as indicated by the exaggerated collimation angle 5 in l lG. ll. In a preferred embodiment of apparatus which has been The con tructed in accordance with my invention, the beam, as it impinges on the target objccl 222. has a collimation half-angle of less than one degree when it is adjusted for an intensity of l3tl watts per square foot. Thus, the collimation half-angle provided by apparatus in accordance with the present invention provides an effective sun as seen by the target object which is only Slightly larger than the sun of our solar system.

Referring again to FIGS. 1, 2 and 3, it may bcobserved that the parabolic collimators 34, 36 and 33 are each shaped to provide a single quadrant of the composite light beam which is directed along thelongitudinal axis of the vacuum chamber to the target object. That is, the lamp 4-4 and its associated parabolic collimator 36 provide a first quadrant portion of the composite light beam. the lamp unit 42 and its associated parabolic collimator -4 prmidc a second adjoining quadrant of the composite light beam, ctc., with four lamps each pro- .viding an individual quadrant shaped light beam to form a composite cylindrical light beam. To that end, each one of the parabolic eollimators 3-3, 36, 3S and 40 is shaped more or less as onequarter of a circle. However, a transtlcctor' 9t) and its associated optical system components, as shown in FlG. ll, will normally provide a cylindrical beam which would slop over the edges of the quadrant shaped parabolic ccllimator 229. It is unde irable to have a portion of the light beam overlapping the edges of the parabolic collimator 220 within he vacuum chamber since such overlapping light energy would generate undesired heat energy. Accordingly, in apreferred embodiment, the shape of the beam provided by a single lamp unit is trimmed by means of a mask 212 located at the first focal plane 211, of the lens 213, and substantially. normal to the longitudinal axis 203 of the optical system. The mask 212 is provided with an approximately quadrant shaped aperture with the aperture being shaped by empirical methods so-that from the off-axis orientation of the parabolic collimator 22ft. The difference in the length of the light paths re- .sults in a slightly greater dispersion of the rays 223 as compared to the dispersion of the rays 225. To compensate for that dispersion and the consequent beam intensity differential, there is provided a graduated screen filter 228, positioned normal to the optical axis 203 and closely adjacent the mask 212. i

As shown in FIG. 12, the graduated screen filter 228 comprises a circular support ring 230 and a large plurality of transversely extending, small diameter wires 231, 232. 233, etc., with the wires 23!. and 232 having a substantially larger inter-wire spacing than do the corresponding wires 2!! and 242 near the right hand side of the graduated screen filter assembly. dia rammatically illustrated in MG. it, the closely spaced portion 24!, 242, 2-13, etc. of the graduated screen filter is positioned below the optical axis 203 with the individual wires 2.41 and 242 oriented in a direction substantially perpendicular to the plane of FIG. ll. Likewise, the more distantly spaced wires 231. 232 and 233 of the graduated screen filter are located above the optical axis 203 (FIG. I I) generally in the region intercepted by the limiting light ray 213. The graduated screen filter operates to at enuate the rays 215 more radically than the rays 213,

thereby compensating for the difference between the lengths of the light paths to the target, and providing for ln the apparatus as substantially uniform intensity across the area of the light beam as it impinges on the target object 222.

As stated heretofore, in some applications of the present invention the size and space limitations which are imposed on the lamp unit 44 (FIG. 1) make it somewhat impractical to position a variable diameter iris diaphragm mechanism such as the element 216 of FIG. 11 at the second focal plane of the transflector 90. In such instances it has been found advantageous to use a different beam intensity controlling device 252 (FIG. 1) positioned about the optical axis 102 of the lamp unit and supported by brackets 254 and 256 which extend outwardly toward the transflector 90 from the mounting ring which secures the entrance port lens 56. One form of the intensity controlling device is shown in FIGS. 14 and 15. The intensity controlling assembly 252 is illustrated in FIG. 13 as comprising a substantially rectangular mounting plate 258 which has a rectangular central aperture 260 for transmission of the light beam. Adjacent the four corners of the aperture 260 are located four small pulleys 262 journaled on cap screws 264 by means of four similar bearings 268. The pulleys 262 are preferably about /8 inch outside diameter with a A; inch groove for carrying a continuous cable 270 which extends in a generally rectangular configuration around the four pulleys and which has its ends secured together by means of a tension spring 272. Intermediate each pair of pulleys 262 the cable 279 is looped around a pulley 274 affixed to a shaft 276. The

three shafts 276 are supported for rotation in like hearing blocks 278 (FIG. 14). Accordingly, the shafts 276 are free to be driven or angularly positioned from time to time by movement of the cable 270. The cable 270 is driven by a fourth pulley 2'74 which is aflixcd to a driving shaft 282 journaled in bearing 278' and having its outer end cou led in a conventional manner to the output shaft 284 of small control motor .286. The motor 236 may be secured in any desired manner to the mounting plate 253, for example by means of the motor mounting bracket 283 as shown in FIG. 14. Energization of the motor 286 rotates the driving shaft 282 to longitudinally shift the cable 270 and thereby rotate the driven pulleys 274. At

the inner end at each of the four driven shafts 276 there is secured a circular disc 290. On the inner face of each disc 298 is carried a triangular radiation absorbing shield 292 having a right angle flange portion 294 which is spotwelded to the circular disc 290. By consideration of the intensity controlling assembly 252 in FIGS. 1 and 13 it may be observed tha the innermost points of the triangular shiclds 292 are located closely adjacent the optical axis 102 of the lamp assembly. The intensity controlling assembly is shown in the wide open" position in which the radiation absorbing shields 292 lie in planes parallel to the central axis 102 of the light beam and therefore have a minimal and negligible effect on the light beam; that is, when the intensity controlling assembly is adjusted to the condition illustrated in FIG. l3, it provides maximum transmission of the light beam from the transllcctor 90 to the entrance port lens 56 and to the target object by way of the collimators 34, 36 and 38. When the driving motor 286 is energized. to rotate the shafts 282 and therefore the four discs 290, the triangular shields or vanes 292 are rotated about their respective axes to gradually reduce the open area of the aperture 260 and thereby gradually reduce the average intensity of the light beam which passes thcrethrough. When. the vanes 292 have been rotated through 90 degrees from the initial position, they reach an orientation as indicated by the dotted lines 296. In this latter position, the radiation shield vanes 292 are positioned in edgcto-cdge contiguous alignment in a single plane normal to the axis of the light beam and therefore completely close the light beam transmissive aperture 260. In order to prevent the intensity controlling assembly 252 from grossly upsetting the uniformity of the light beam it is desirable to locate the assembly at a position along the optical axis as far as possible from Lil . light controlling device.

other form of the intensity controlling devices places the triangular light blocking shields along the perimeter of the circular disc 290. In this position the shields move completely out of the light beam in the full open position. Thus no light loss occurs because of the presence of the uniformity does occur but is not of sufficient magnitude to seriously disturb the over-all performance of the apparatus as a means for simulating outer space conditions. In a preferred embodiment of my invention the control motor 286 is energized and driven by a small servoamplitier (not shown) which is in turn controlled by the output of a semiconductivc photodetcctor or solar cell 298 or the like which is located within the vacuum chamber on the back surface of the collimator 36. A small aperture is provided in the collimator 36 so that a small portion of the light beam falling on the collimator passes through the aperture and impinges on the solar cell 298 to generate a control signal substantially proportional to the average beam intensity. The electrical circuitry including photodetector 0r solar cell 298, the servo-amplifier and its connections to the drive motor 286 may take any one of a large variety of conventional forms. and, accordingly, is not disclosed in detail.

While the transllector light collecting apparatus as described heretofore is much more satisfactory from the beam uniformity and efficiency standpoint than the various light collecting mirrors which have been previously used with are lamps, it nevertheless collects light from only a solid angle of about 140 degrees and therefore discards a substantial amount of light energy originally generated by the carbon arc. Any arrangement which will increase the light collecting'capacity of the trans- Ilector will be a boon to the solar simulation facilities in that it will reduce the operating costs and the initial costs of the power supply components which must be provided for a high energy system. To that end there is illustrated diagrammatically in FIG. 15 a further embodiment in accordance with the present invention in which the light collecting capability of the transflcctor is augmented by provision of an auxiliary rellcctive ring associated with each ring of the transtlcctor. Specifically, as shown in FIG. 15, the transllector device comprising rings 35!, 352, 353, etc. and lens 360 is oriented in the usual manner concentrically about the longitudinal axis 370 of the light beam path. The system of FIG. 15 is gcncrally similar to that illustrated in FIG. ll in thata projection lens 363 is located at the second focal plane of the transllcctor and a parabolic collimator 372 is positioned with its midpoint substantially at the intersection of the central axis 370 and the image plane 374. This embodiment differs from that illustrated in FIG. 11 in that the larger diameter rings 351, 352., 353, 354 and 355 each has an auxiliary ring 3510, 3520, etc. attached to the larger diameter edge thereof. That is, the auxiliary rings are attached to the edge of the primary rings which are closest to the source 350 in the axial direction. These auxiliary rings are also substantially conically shaped and have high specular inside surfaces for ctlicicntly rellccting the light which impinges thereon from the source 350. The auxiliary rings collect some of the light energy which would otherwise be lost by transmission through the inter-ring apertures and rellcct that supplementary light energy from the surface 35in, for example, to the surface 351 which, in turn, reflects the supplementary light along a beam path portion indicated by the limiting rays 362 and 266. Thus, each auxiliary ring 351a, 35211,

Some deformation of-the beam etc., augments the etliciency of a particular primary ring 351, 352, etc. The optical effect of the auxiliary rings is to broaden the focused light beam which impinges on the projection lens 368 with the broadening being sub stantially proportional to the amount of supplementary light energy which is collected from the source 350. The projection lens 368 reproduces the augmented composite beam at the image plane 374 where the supplementary light energy appears only as an increase in the beam intensity. The foregoing described embodiment in accordance with the present invention requires a projection lens 368 which is somewhat larger than the corresponding lens of the apparatus of P10. 11. Also, the collimation angle 5 is increased in direct proportion to the increase in the intensity of the light beam. For many applications the increased size and cost of the projection lens 368 is readily justified by the over-all cost reduction which results from an improvement in etiieiency. Likewise, in many solar simulation facilities a slight increase in collimation angle, such as that which results from this latter embodiment, is acceptable for the particular simulation purposes which are contemplated.

It will be appreciated from all the foregoing that my invention provides a system for simulating the thermal conditions which are encountered in outer space or at high altitudes, which system is highly advantageous in a number of respects as compared to systems for the same purpose which have been previously used and proposed.

Specific-ally, among the comparative advantages of one The final light beam intensity is constant at all planes normal to the longitudinal axis of the vacuum chamber. There is no intensity variation with variation of the distance of the test object from the parabolic collimators 3436. There is no gross variation in the beam intensity such as that which occurs in some systems as a result of overlapping of the light beams from separate lamp units. In one apparatus which has been constructed and successfully used, intensity variations resulting from impcrfections of the system are less than i-5%.

The off-axis arrangement of the parabolic collimators 34, 36 and 38 prevents degradation of the heat sink characteristics of the vacuum chamber. That is, the target object or aerospace vehicle which is being tested can see" only the cold walls of the chamber or the simulated sun which is represented by the impinging light beam. Thereis no reflective surface within the chamber from which radiation emitted by the target object can return to the target object. This feature of systems in accordance with my invention is particularly desirable and advantageous as compared to beamforming systems employing Cassegrainian optical systems which systems inherently introduce an error by permitting the target object to see itself in the collimating mirrors of the optical system.

Systems in accordance with my invention have an unusually high cthcieney resulting from the novel transtlcctor light collecting arrangement and from the fact that the mechanisms for holding and feeding the positive and negative carbons are disposed in positions substantially outside the light path from the are to the transflector. The improved light collection efficiency enables a single lamp unit to cover a much larger area of a'targct object with one sun intensity levels. This, of, course, results in a relatively low initial cost as compared to systems having lower light generation eflicicncics.

While the present invention has been shown in one form only, it will be obvious to those skilled in the art that it is not so limited but is susceptibic of various changes and modifications without departing from the spirit and scope thereof.

The embodiments of the invention in which an excluall to sire property or privilege is claimed are defined as f0l lows: i

1. la a light projection system: reflecting in ans having a proximate focus and a remote focus and a longitudinal axis of symmetry extending thcrcbetwccn; I a light source positioned substantially at said proximate focus; said reflecting means comprising a plurality of ringshapcd conic section reflector elements of unequal mean diameters, each of said connic section reflector elements being a conic approximation of a segment of an ellipsoid which is a member of a family of ellipsoids having foci substantially at said proximate focus and said remote focus; each of said reflector elements having a width in the axial direction substantially smaller than the minimum straight line distance from the same element to said light source; each of said reflector elements being concentrically positioned about said axis so that their respective mean diameter circles lie in axially spaced apart lanes normal to said axis. with the plane of the smallest diameter rttlcctor element being spaced the greatest axial distance from said prcximatc focus and the successively larger diameter reflector elements being respectively positioned at such lesser axial distances from said proximate focus that the radial distances from said light source to the mean diameter circles of said reflector elements are substantially the same whereby all said portions are illuminated with light of approximately the same intensity. 2. In a light projection system: a light source; reflecting means formed of a group of annular segments of substantially ellipsoidal surfaces, said segments having substantially coincident proximate and remote foci and having boundary edges defined by parallel planes normal to the longitudinal axis which includes said foci; said segments having respectively different mean diameters, with the segment having the smallest diameter being most distantly spaced along said axis from the proximate focus and with the segments of successively larger diameters being indivdually axially posi-' tioned more closely adjacent said focus so that light from said sourceimpinging on the inner surface of a given one of said larger diameter segments is reflected therefrom, through the interstitial space between said one segment and the next smaller diamctcr segment, toward the remote focus, the radial distances from said light source to the mean diameter circles of said segments are substantially the same whereby all of said segments are illuminated with light of approximately the same intensity, each of said segments having a width in the axial direction substantially smaller than the minimum straight line distance from the same segment to said light source.

3. in a sunlight simulating system for uniformly irradiating a predetermined area of a target object:

a carbon arc radiation source;

a multisurfacc reflective means positioned to receive radiationfrom said source for directing a beam along a predetermined axis to illuminate said object;

said retlcctive means comprising a plurality of concentrically arranged, annular reflective surfaces with each surface having a curvature substantially corresponding to a segment of an ellipsoid and with each reflective surface having a width in the axial direction which is relatively small compared to the distance from the same surface to said source;

said difl'crcnt annular surfaces being differently spaced from said source along said axis in a manner such that the different light paths from said source to dill'ercnt ones of said rctlcctire surfaces are of approximatcly the same optical length and such that the beam path length from a given portion of any one of said reflective surfaces to said target object is longer than the path length from a corresponding portion of any other one of said reflective surfaces which has a lesser mean diameter.

4. In combination:

a light source;

a target member to be illuminated by radiation derived from said source;

a light path extending from said source and including at least one portion having a central axis which extends through said source;

a light collecting means disposed adjacent said source for gathering a substantial portion of the light emanating therefrom and directing the same along said path, said means comprising a plurality of ring-like reflective surfaces with each of said surfaces being symmetrically disposed relative to said axis; and

each of said surfaces having a radial cross section which substantially corresponds to a chord of a segment of one ellipse of a family of ellipses having the same foei, with each of said surfaces having an axial direction width that is substantially smaller than the straight line distance from the same surface to said light source;

said different surfaces being spaced along said axis at different positions such that corresponding portions of the ditl'erent surfaces are approximately equidistant from said radiation source and so that light reflected by the larger diameter one of said surfaces is constrained to follow a substantially cylindrical outer path portion which peripherally encompasses the smaller diameter surfaces.

5. A beam forming light projection system comprisin light source;

a target to be illuminated by radiation derived from said source;

a light path extending from said source andincluding at least one portion having a central axis which extends through said source;

a light collecting means disposed adjacent said source for gathering a substantial portion of the light emanating therefrom and directing the same along said path, said means comprising a plurality of reflective surfaces with each of said surfaces being symmetrically disposed relative to said axis;

each of said reflective surfaces having an axial direction width substantially smaller than the minimum straight line distance from the same surface to said light source;

each of said surfaces having a radial cross-sectional form which substantially corresponds to a segment of a different one of a plurality of elliptical curves with all said elliptical curves having the same proxitil Ill)

mate and remote foci and with all said surfaces being spaced at approximately the same radial distance from said soutce so that the d tl cicnl light paths from said soutcc to different ones of said surfaces are all substantially the same length and the light from said source is; substantially uniformly distributed over a predetermined area of said target member; and

said rcllective surfaces being axially spaced apart in a region between a first plane which pcrpemlicularly intercepts said light source and a second plane which perpendicularly intercepts said light path at a distance from said light source which slightly exceeds the polar distance from said source to said reflective surfaces.

6. A high intensity beam forming lamp comprising:

a light source:

a light path extending from said source and including at least one portion having a central axis which extends through said source;

a light collecting means disposed adiacent said source for gathering a substantial portion of the light ema- 'nating therefrom and directing the same along said path in the form of a collimated beam;

said means comprising a plurality of annular reflective surfaces with each of said surfaces being symmetrically and concentrically disposed relative to said axis;

each of said reflective surfaces having an axial direction width substantially smaller than the minimum straight line distance from the same surface to said light source;

each of said surfaces having a form which substantially corresponds to a segment of adilfercnt one of a family of ellipsoids which have the same proximate and remote foci, and with all said surfaces being spaced at approximately the same radial distance from said source so that the different light paths from said source to different ones of said surfaces are all substantially the same length and the light from said source is substantially uniformly distributed over the cross sectional area of said light path;

said annular rellectivc surfaces having different mean diameters with the surface having the largest diameter being positioned the least axial distance from said source and with the surfaces having successively smaller diameters being respectively more remote from said source along said axis.

References Cited by the Examiner UNITED STA'Il'iS PATENTS 1,699,108 1/1929 llalvorson 88-24 1,791,713 2/1931 Dye et al. 24046.41 1,864,696 6/1932 Steele ct al. 8824 2,7l6,l83 8/1955 Stcbbina 2 l()4l.35 3,064,364 1 H1962 Schucllcr.

NORTON ANSllER, Iri/lmry Examiner. 

2. IN A LIGHT PROJECTION SYSTEM: A LIGHT SOURCE; REFLECTING MEANS FORMED OF A GROUP OF ANNULAR SEGMENTS OF SUBSTANTIALLY ELLIPSOIDAL SURFACES, SAID SEGMENTS HAVING SUBSTANTIALLY COINCIDENT PROXIMATE AND REMOTE FOCI AND HAVING BOUNDARY EDGES DEFINED BY PARALLEL PLANES NORMAL TO THE LONGITUDINAL AXIS WHICH INCLUDES SAID FOCI; SAID SEGMENTS HAVING RESPECTIVELY DIFFERENT MEAN DIAMETERS, WITH THE SEGMENT HAVING THE SMALLEST DIAMETER BEING MOST DISTANTLY SPACED ALONG SAID AXIS FROM THE PROXIMATE FOCUS AND WITH THE SEGMENTS OF SUCCESSIVELY LARGER DIAMETERS BEING INDIVIDUALLY AXIALLY POSITIONED MORE CLOSELY ADJACENT SAID FOCUS SO THAT LIGHT FROM SAID SOURCE IMPINGING ON THE INNER SURFACE OF A GIVEN ONE OF SAID LARGER DIAMETER SEGMENTS IS REFLECTED THEREFROM, THROUGH THE INTERSTITIAL SPACE BETWEEN SAID ONE SEGMENT AND THE NEXT SMALLER DIAMETER SEGMENT, TOWARD THE REMOYR GOCUS, THE RADIAL DISTANCES FROM SAID LIGHT SOURCE TO THE MAIN DIAMETER CIRCLES OF SAID SEGMENTS ARE SUBSTANTIALLY THE SAME WHEREBY ALL OF SAID SEGMENTS ARE ILLUMINATED WITH LIGHT OF APPROXIMATELY THE SAME INTENSITY, EACH OF SAID SEGMENTS HAVING A WIDTH IN THE AXIAL DIRECTION SUBSTANTIALLY SMALLER THAN THE MINIMUM STRAIGHT LINE DISTANCE FROM THE SAME SEGMENT TO SAID LIGHT SOURCE. 